1. Field of the Invention
The present invention relates to a through-the-lens or interior-light-measurement type automatic exposure control system for a single lens reflex camera, and more particularly it pertains to an automatic exposure control system which controls exposure time in accordance with an output from a light measuring device that measures scene light or object light passing through the camera objective and reflected from the film surface.
2. Description of the Prior Arts
A camera exposure control system is known which controls exposure time as a function of scene light passing through the camera objective and reflected from the film surface and/or a surface of a focal plane shutter member having practically the same light reflection characteristics as those of the film surface. Such an exemplary camera exposure control system is shown in U.S. Pat. No. 3,687,026, the disclosure of which is incorporated herein by reference.
The exposure control system of the film-reflection-light measuring type as mentioned above has many advantages over other types of exposure control systems. For instance, through-the-lens light measurement can be carried out simultaneously with film exposure. The scene light is detected by that part of the light to which the film is currently being exposed. This may be compared with a storage type exposure control for single lens reflex cameras wherein a light measuring circuit measures the scene light through the camera objective prior to film exposure. The output from the light measuring circuit is stored in a storage device such as a capacitor before the light measuring photocell is blocked from the scene light by the movement of the reflex mirror from its viewing to photographing position, so that exposure is controlled in accordance with the stored output.
Further, simultaneous or real time light measurement by film-reflection-light type measurement enables the amount of light emitted from an electronic flash device to be controlled in accordance with through-the-lens type light measurement, since the flash light to be measured and controlled is produced during a camera exposure. This flash control is effective particularly in close-up photography and bounce light photography.
Also, film-reflection-light type measurement has an advantage that the measurement is not affected by the light entering from the view-finder eyepiece when it is employed in a single lens reflex camera, because the reflex mirror of the camera at its photographic position blocks such light during film exposure when the light measurement is taking place.
However, such light measuring type systems do not perform the function of storing the measured values as is done by the storage type exposure control systems. It is sometimes desirable that exposure is controlled in accordance with light measurement carried out separately from the film exposure, for an object portion and at the time selected by the photographer. For example, the photographer may wish to take a picture with an exposure condition suitable for a particular portion of a scene which is not covered by the light acceptance angle of a photocell when the camera is aimed at the scene, or which is smaller than the area covered by the light acceptance angle. With the storage type exposure control system, light measurement taken with the light acceptance angle being matched with the desired portion of the scene may be fixed independently of the film exposure by manually causing storage of the light measurement signal, and exposure may be controlled in accordance with the stored measurement signal.